1. State Key Laboratory of Luminescent Materials and Devices and Institute of Optical Communication Materials, South China University of Technology, Guangzhou 510641, P. R. China
2. Key Laboratory of Rare Earth Optoelectronic Materials and Devices of Zhejiang Province, Institute of Optoelectronic Materials and Devices, China Jiliang University, Hangzhou 310018, P. R. China
3. School of Physics and Optoelectronics, South China University of Technology, Guangzhou 510641, P. R. China